This invention relates to a safety locking device for a quick hitch/coupler.
Quick hitches or couplers are used with earth working machines such as excavators whereby an implement such as a bucket can be quickly coupled to or removed from the earth working machine. The quick hitch can thus be attached to the end of the excavator arm.
The quick hitch has a hook portion which is engageable with the so-called “front pin” of an implement. A mounting portion of the quick hitch can then be engaged with the “back pin” of the implement following which a mechanism in the quick hitch is operated to retain the back pin in the mounting portion. When the back pin is so locked into position the front pin is prevented from moving out of the hook portion.
Such quick hitches are widely known and used. The mechanism to lock the back pin in place can take different forms but, in one form, can be a wedge which is moveable by a hydraulic ram. A construction of quick hitch with a wedge mechanism is shown in our New Zealand patent specification nos. 233302 and 260659.
The quick hitch permits the operator of an earth working machine to attach and remove implements without moving from the cab or operating position of the machine. However, a problem that can arise is that the operator may move the part of the machine to which the quick hitch is attached (e.g. an excavator arm) before the back pin is fixed into the mounting portion or the locking mechanism is operated before the back pin is in position in the mounting portion. This can happen because experienced operators tend to position a quick hitch with the implement, lock the quick hitch and move the implement all in one fluid action. Therefore there is the possibility of the operation not being carried out correctly with the result that the implement is not fully locked into the quick hitch.
If incomplete mounting occurs the implement may, when moved, i.e. lifted off the ground, fall from the quick hitch. This creates a situation where damage to the implement can occur or, more seriously, personal injury or death of a bystander can occur due to the uncontrolled movement (falling) of the implement.
It is known to provide in a quick hitch a safety locking device for the front pin so that if incomplete fixing of the back pin occurs, the implement will nevertheless still remain attached by the front pin. These known devices have, however, suffered from drawbacks. For example the safety device may not be failsafe i.e. automatically engage upon the front pin engaging in the hook portion of the quick hitch.
Furthermore many known safety lock devices are controlled by the hydraulic circuit that operates the primary locking mechanism. Sometimes these safety lock devices are mechanically sequenced with the primary locking mechanism which is hydraulic. Thus a failure in the primary locking mechanism hydraulics (allowing unintentional release or movement of the primary locking jaw or wedge from the back pin) could result in the safety lock failing simultaneously due to it being sequential. Thus a failure in the safety lock device hydraulics could result in the locking mechanism failing with potentially disastrous results if this leads to the implement falling from the quick hitch. For example, if there is a seal failure in the ram of the primary locking device, this can result in hydraulic fluid bypass which may cause the hydraulic ram of the locking mechanism to fail to maintain locking of the back pin.